The present invention relates to suspension strut assemblies for use in vehicle suspension systems and more particularly to such struts which incorporate fixed and variable rate spring means in combination with friction damping apparatus.
Strut type suspension systems are being incorporated into more and more of our present day motor vehicles in order to accommodate the demands for lighter more compact fuel efficient vehicles. One of the more common of these strut suspensions utilize a MacPherson type strut which incorporates conventional constant rate helical coil springs in conjunction with hydraulic type shock damping means.
Such struts have many disadvantages associated therewith in spite of their compactness and relative weight savings over prior conventional suspension systems such as for example high replacement costs, numerous seals for the hydraulic damping arrangement, binding or sticking of internal bearings, etc. Additionally, because these struts employ substantially constant rate helical coil springs, vehicle ride frequency, which is a function of both mass and spring rate, may only be optimized for one particular load condition. Thus, at any other load condition the ride frequency must be compromised and less than optimum. This comprise is becoming increasingly more significant as the total weight of vehicles is decreased. While previously a conventional passenger car may have weighed approximately four to five thousand pounds, present day vehicles are more likely to fall within a range of two to three thousand pounds. Thus, whereas with the prior heavier vehicles the difference between operating the vehicle lightly loaded such as with only the driver versus heavily loaded such as with four to six people plus luggage or the like may have represented a relatively small percentage increase in load on the suspension system, the same difference in loading represents a substantially more significant percentage increase in loading for the present day lighter weight vehicles. Hence, the load range of present day vehicles as a function of vehicle weight has increased significantly. Because the ride frequency is a function of both the spring rate and the sprung mass, it is substantially more difficult, if not impossible, to provide a comfortable vehicle ride at both light load levels and full load levels in today's lighter weight vehicles particularly with conventional coil spring suspension systems.
Accordingly, the present invention provides an improved suspension strut assembly particularly well suited for use in conjunction with such lighter weight fuel efficient motor vehicles which provides both variable and fixed rate spring means whereby the optimum vehicle ride frequency may be more closely approximated over a substantially greater range of vehicle loading from relatively light loading to substantially full vehicle loading. Additionally, the improved strut assembly of the present invention utilizes a friction damping arrangement which reduces the number of parts required for the assembly as well as offering improved reliability due to the elimination of numerous hydraulic seals required in conventional damping systems. Further, not only does the use of a friction damping system offer substantial cost savings by requiring fabrication and assembly of fewer parts but also the need for high tolerance machining operations necessary to provide the metered fluid flow ports and the like in hydraulic damping arrangements is also reduced thereby affording additional cost savings.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.